1. Yes. Depending on times of year I have experienced Orcas (Very rare though), seals, sharks and all the little different critters. All within recreational depths.
2. Yes. Frankenwald, Fernedale&Parat (spectacular double wreck with safety/decostops on a gorgeous "sailrock" littered with anemones and critters), Havda, Welheim and Bandak are among the wrecks that can be done recreationally.
3. Best time depends of your cold-tolerance. Winter months (dec-feb) has best visibility, but water dips to lowest at about 6C in March. Spring/Autumn usually have an algaebloom. Late summer/fall has reasonable good visibility 15ish meters with comfy temperatures of about 20ish in the surface in August.
4. Cold to coldish all year. This is definitely dry suit territory.
5. Yes! Ålesund, Sunnmøre, Trøndelag (which has afaik the only cold water coral reef in diveable depths (recreationally), Hitra, Bergen, Lofoten, Kristiansand.
Ålesund is famous for technical(and a bit rec) wreckdiving.
6. Extra info: Keep in mind, Norway IS dry suit country. It is cold(ish). Diving is VERY independent. There will NOT be a guide in the water. You will be given a LOT of freedom, and you are expected to deal with it. Norway has "common sense" laws. (Ie, not the kind of liabilitystuff as in the states). There are few dive shops, fewer dive centres, and a lot of dive clubs. Most of the clubs are very welcome to strangers, but equipment can be hard to source. Make sure you have travel-insurance. While Norway has a very good health care system, unless you are European, you will get a bill afterwards. However, you will get treated first. Hyperbaric centers are few and very far apart. Distances are long, and EMS takes time to get to you. Plan accordingly. Dive conservatively.